The present invention relates generally to an anti-skid brake control system for an automotive vehicle. More particularly, the invention relates generally to an anti-skid brake control system, in which a vehicle speed representing value is derived on the basis of a wheel speed. Further particularly, the invention relates generally to an anti-skid brake control system which prevents all of wheels from locking simultaneously and whereby assures derivation of the vehicle speed representing value precisely corresponding to an actual vehicle speed for assuring accurate brake control even on substantially slippery road condition.